JPS6064580A - Automatic aperture controller of lens for cctv camera - Google Patents

Abstract

PURPOSE:To attain optimum aperture control at all times even if an output of a picture signal differs depending on the absolute brightness of an object or difference of types of a camera. CONSTITUTION:A resistance value of a variable resistance VR1 is constituted to be freely slidable so that the value can be set lower when an optimum picture signal level of a camera is high and an input VIN is large and can be set higher when the picture output level of the camera is low and the input VIN is small conversely, for example. Moreover, a part of a picture signal corresponding to a light part is limited by adjusting a DC voltage fed to a remote terminal or a variable resistance VR2 in a limiter circuit II, whether a bright part is used as a major object or the dark part is used as the major object is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic diaphragm control device for lenses used in CCTV cameras, which are widely used.

When controlling the aperture of a lens using an image signal from a television camera, there are cases where the image signal can be rectified as is and used as a control signal, but the absolute brightness of the subject varies. The image signal level also increases or decreases accordingly, and depending on the type of camera, the image signal may be originally large or small. In such cases, it is necessary to control the aperture by controlling the image signal from the camera. Unless it is used as a signal, an optimal image cannot be obtained. In addition, the range of contrast, the brightness ratio between bright and dark parts of a subject, is, for example, in the natural world, even on cloudy days, in the tens of twenty-ones, and on clear skies it can reach several hundred = one, whereas it is reproduced on television. The contrast display range of the resulting image is only about 30 to 40:1. Therefore, in order to obtain an optimal image in the natural world, it is necessary to control the ratio of the bright portion of the camera image signal to the entire screen and use it as an aperture control signal. Also, if these aperture signals cannot be stably obtained over a wide range of power supply voltage,
It is not possible to stably control the aperture of the various CC and TV camera lenses that are used frequently.

Therefore, the present invention was made to solve these problems.The gist of the present invention is to provide an automatic aperture control device that controls the aperture of a lens using image signals from a television camera. a first means for continuously controlling an image signal for a subject; and a second means for continuously controlling an image signal for a bright part occupying the entire screen when the contrast ratio between the bright part and the dark part of the subject is relatively high. and the means of
and third means for stabilizing the control signal obtained by rectifying the image signal obtained by the means with respect to the power supply voltage.

The present invention will be described in detail with reference to the embodiments illustrated below.
In FIG. 1, 1 is an image signal Vi from a television camera.
This is an input terminal for inputting signal n, and is connected to the ground side 4 via a resistor R1, and is also connected via a capacitor C4 to an inverting amplifier circuit (2) constituting the first means of the present invention. In the inverting amplifier circuit I, the inverting input terminal 11 of the operational amplifier AI is connected to the capacitor C1 via a resistor R2, while the non-inverting input terminal 12 is connected to a midpoint voltage terminal 2, which will be described later, via a resistor R3. A variable resistor VRI as a feedback resistor is provided between the inverting input terminal 11 and the output terminal 13. This inverting amplifier circuit l is configured to invert and amplify the image signal Vin from which the direct current component has been removed using the capacitor C1, and obtain an inverted amplified signal Vac at its output terminal 13. By adjusting the variable resistor VRI, The first means of the present invention has a configuration in which the gain (amplification factor) of the operational amplifier Al can be changed continuously. In other words, increasing the resistance value of the variable resistor VRI increases the gain, and conversely decreasing the resistance value decreases the gain. Therefore, in FIG. 2, for example, the optimal image signal of the camera is high and the input image signal Vin is high. In this case, the input change amount γ becomes large, but in such a case, the resistance value is adjusted to be small to reduce the gain, and conversely, when the input change amount T of the image signal Vin is small, the resistance value is increased. The structure is such that the gain can be adjusted to increase by increasing the gain, so that an inverted amplified signal Vac with a constant output variation can always be obtained.

(2) is a limiter circuit that continuously limits the output of the negative side of the image signal inverted and amplified by the operational amplifier A1 (the image signal output corresponding to the bright part of the entire screen), which implements the second means of the present invention. It consists of The limiter circuit (2) is provided in parallel with the variable resistor VRI, and includes a diode D1 and a variable resistor V that controls the current flowing through the diode D1.
Consisting of R2 and a switching transistor Tri,
The inverting input terminal 11 of the operational amplifier A1 and the anode of the diode D1 are connected, and the cathode and the output terminal 13 are connected.
and are connected via a variable resistor VR2.

Furthermore, the switching transistor TRI connects the variable resistor VR2 to remotely control the diode D1.
The base and remote terminal 3 are connected via a resistor R4.

This limiter circuit (2) is configured to obtain input/output characteristics in which the negative side of the output voltage of the operational amplifier A1 is forcibly suppressed by the diode DI, as shown by the solid line (2) in FIG. That is, in FIG. 3, the horizontal axis represents the operational amplifier A1.
The vertical axis shows the output voltage V13 of the output terminal 13, and the input voltage Vll is α
When it is larger, the output voltage V13 becomes constant at β and has a limiter characteristic. Note that the broken line (1) shows the original characteristics when the limiter is not activated.

The inverted signal Vac obtained by the above-mentioned inverting amplifier circuit (2) is rectified by the subsequent voltage doubler rectifier circuit. The voltage doubler rectifier circuit is
A voltage doubler capacitor C2 is connected to the output terminal 13 of the operational amplifier AI, the output terminal of the capacitor C2 and the midpoint voltage terminal 2 are connected via a diode D2, and a diode is connected to the output terminal of the capacitor c2. D3 is connected in the forward direction to obtain a rectified signal Vdc. c.
3 is a capacitor installed between the ground side 4 and the rectified signal Vdc to level it out.

(2) is a stabilizing circuit that stabilizes the rectified signal Vdc with respect to the power supply voltage VCC, and constitutes the third means of the present invention. In the stabilizing circuit (■), first, series resistors R8 and R9 are installed between the positive voltage side 5 and the ground side 4, and by connecting the middle of these resistors R8 and R9 to the midpoint voltage terminal 2, the power supply voltage is adjusted. (2) It is configured to output a voltage vO midway between cc and cc to the midpoint voltage terminal 2. In the case of the example,
The most preferable configuration is to set R8 and R9 to be equal and output a voltage VO that is 1/2 of the power supply voltage Vcc to the midpoint voltage terminal 2. Further, from the positive voltage side 5 to the ground side 4, a resistor R6, a Zener diode D4, a resistor R
7 are connected in sequence, and the output end of the voltage doubler rectifier circuit is connected between the Zener diode D4 and the resistor R7.
, and lower the rectified signal Vdc by a certain voltage to the negative side, so that the range of behavior of the rectified signal Vdc can be level-shifted so as to span the plus and minus sides based on the midpoint voltage 0. It is composed. In the example, resistors R6 and R7 are set equal, and the Zener voltage V
2 is configured so that it is equal to both the positive and negative voltages with respect to the midpoint voltage (2) 0. That is, as shown in FIG.
Even if the midpoint voltage VO (Vcc/2 in the embodiment) increases as the power supply voltage Vcc increases, the Zener voltage Vz
The voltage Vs, which is reduced by half of the voltage, is in a constant voltage reduced relationship with respect to the midpoint voltage, and the voltage difference Vs between the midpoint voltage and the rectified signal Vdc is stable in a constant relationship regardless of changes in the power supply voltage Vcc. It is configured to be

The rectified signal ■dc level-shifted by the stabilization circuit ■ is
It is connected to the inverting input terminal 21 of the operational amplifier A2 of the circuit in question via a resistor RIO, and a resistor R11 is provided as a feedback resistor between the output terminal 23 of the operational amplifier A2 and the inverting input terminal 21. It is. Furthermore, the non-inverting input terminal 22 and the midpoint voltage terminal 2 are connected via a resistor R12, and the rectified signal Vdc is compared with the midpoint voltage 0, and the control signal VOUT is obtained at the output terminal 6. It is configured so that it can be used.

To explain the operation mode of the present invention based on the embodiment having the above configuration, the image signal Vin from the television camera is
Assume that a waveform as shown in FIG. 5(b) corresponding to the test chart of FIG. 5(a) is input to the input terminal 1. In this waveform, the rectangular part on the positive side corresponds to the bright part of the image,
Vd indicates the image level, and Vs indicates the synchronization level. The DC component of this image signal Vin is removed by the capacitor C1, and as shown in FIG. 6, the image signal Vin is balanced so that the area on the plus side and the minus side with respect to the reference voltage V are equal, as shown in FIG. This signal is applied to the midpoint voltage terminal 2 by the inverting amplifier circuit I.
With reference to the midpoint voltage ■0 supplied from
), the signal is inverted and amplified, and becomes an inverted signal Vac at its output terminal 13.

The gain (amplification factor) of this inverting amplifier circuit I is determined by the ratio of the resistance value of the variable resistor VRI to the resistor R2, so if you adjust the variable resistor R1 and increase the resistance value, the gain will also increase, and the amplitude of the inverted signal Vac. When Vac increases and decreases, the gain also decreases, and the amplitude of the inverted signal Vac decreases. Therefore, even if the optimum image signal from the television camera is too large or too small, the variable resistor VR
With I, it is possible to always obtain a constant amount of output change,
This is the first means of the present invention.

Next, in the limiter circuit H, by adjusting the variable resistor VR2 near the camera or the remote remote terminal 3, the part corresponding to the bright part of the image signal is limited, and it corresponds to the brightness ratio of the image in the natural world. Accordingly, the second means of the present invention can be used to control whether a bright place or a dark place is the main subject. First, when adjusting the variable resistor VR2, if the resistance value is made infinite, the limiter circuit ■ will not work, so
The inverted signal Vac has a waveform similar to that shown in FIG. 7(a). When this inverted signal Vac is input to the capacitor C2 of the voltage doubler rectifier circuit, the diode D2 becomes conductive due to the negative side signal, charging the capacitor C2, and the subsequent positive side signal is added, resulting in the voltage doubler signal as shown in Figure 7. As shown in FIG. 5B, the amplitude is directly reproduced as it is, and a control signal suitable for setting the bright part where the image level Vd of FIG. 5B is detected as the main object is obtained.

Next, when the resistance value is set to 0, the diode D1 becomes conductive, and a limiter is applied to the operational amplifier AI, as shown in (2) of FIG. The part is cut and the inverted signal Va without the dashed line part
When this inverted signal Vac is rectified by a voltage doubler rectifier circuit, direct current is regenerated as shown in FIG. 8(b) as in the previous case. In this case, the rectified signal is obtained by canting the signal of the bright part of the image signal Vin and has a value close to the average of the entire amplitude, so that a control signal suitable for making the dark part the main subject can be obtained. Furthermore, it goes without saying that an intermediate control signal can be obtained by setting the variable resistor VR2 to an intermediate resistance value.

Next, input the mote voltage to remote terminal 3.
The switching transistor T'RI turns on, the diode D1 becomes conductive, and the operational amplifier circuit I is put in a limiter state. Therefore, using the remote terminal 3, it is possible to remotely control whether the main subject is a bright part or a dark part.

Next, the rectified signal Vdc that has passed through the voltage doubler rectifier circuit is
As shown in the figure, the Zener voltage Vz of the stabilizing circuit (2) causes the midpoint voltage VO (Vcc/2) to be lowered by a constant voltage Vs. This means that the rectification multiplication %Vdc is positive with respect to the midpoint voltage vO even in the darkest condition because the synchronization level Vs originally exists in the image signal Vin, so if this is directly compared with the midpoint voltage ■0 If a control signal is obtained by using the same method, a sufficient control signal for the dark image signal Vin cannot be obtained. Therefore, by lowering the voltage of the rectified signal Vdc to the negative side by a certain voltage, the dark image signal becomes negative with respect to the midpoint voltage VO. This means that an appropriate control signal is obtained by adjusting the rectified signal Vdc as a whole so that the range of behavior of the rectified signal Vdc is the same on both the plus side and the minus side with reference to the midpoint voltage (2) 0.

This rectified signal Vdc is input to the inverting input terminal 21 of the operational amplifier A2 of the comparator circuit, and is compared with the midpoint voltage VO (Vcc/2) obtained from the stabilizing circuit (2), and a control signal is sent to its output (16). VouL will be obtained. At this time, if the image state is optimal, the rectified signal Vdc (V21
) is equal to the midpoint voltage ■0, and the output voltage V23 becomes VO, so Vout is O and no aperture control is performed. When the subject is bright and the input voltage V21 is larger than ■0,
The output voltage V23 becomes smaller than ■0, so Vou
t becomes a negative aperture control signal that closes the aperture. Further, when the subject is dark and the input voltage Vdc (V21) is smaller than 0, the output voltage V23 becomes larger than the midpoint voltage VO, and therefore, Vout becomes a positive aperture control signal that opens the aperture.

As described above, according to the automatic aperture control device for a CCTV camera lens according to the present invention, even if the image signal input from the camera varies in size depending on the absolute brightness of the subject or the type of camera, it can continuously process the image signal. It is possible to obtain an aperture control signal that can be controlled to obtain an optimal image.Also, by limiting the image signal portion corresponding to bright areas according to the brightness ratio (contrast) of the subject, the main subject can be It is possible to obtain an aperture control signal that can be selected for bright or dark areas to obtain an optimal image signal, and furthermore, by stabilizing the aperture control signal for a potential that is half the power supply voltage, normal stabilization can be achieved. This has the effect of being able to perform aperture control over a wide voltage range that would be unimaginable with a circuit.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 shows a circuit diagram of an embodiment of the device of the present invention,
Fig. 2 is an explanatory diagram explaining the action of the first means;
FIG. 4 is an explanatory diagram explaining the action of the second means, FIG. 4 is an explanatory diagram explaining the action of the third means, FIG. 5 is an explanatory diagram showing the relationship between the subject and the image signal, and FIG. 7 and 8 are schematic explanatory diagrams of input waveforms before control by the means of the present invention.
The figure is a schematic explanatory diagram illustrating control waveforms by means of the present invention. 1... Image signal input terminal 2... Midpoint voltage terminal 3... Remote terminal 6... Control signal output terminal ■... Inverting amplifier circuit (first means) ■... Limiter circuit ( 2nd means) ■... Stabilization circuit (3rd means) 2nd Figure 11\□ Large 3, A'''1'86°゛゛'' 71i! l (+) (-) Figure 8 (-)

Claims (4)

[Claims] (1) In an automatic aperture control device that controls the aperture of a lens using an image signal from a television camera, a first means for continuously controlling the image signal with respect to the absolute brightness of the subject; a second means for continuously controlling an image signal for a bright part occupying the entire screen when the contrast ratio between the bright part and the dark part is relatively high; and control obtained by rectifying the image signal obtained by the said means An automatic aperture control device for a CCTV camera lens, comprising a third means for stabilizing the signal with respect to the power supply voltage. (2) In the device according to claim fl), the first control unit lowers the gain when the optimum image signal level of the television camera is high, and increases the gain when the optimum image signal level of the television camera is low. An automatic aperture control device for a CCT camera lens, which is characterized by comprising a means for achieving uniform input and output characteristics. (3) A CCTV camera characterized in that the device according to claim 11 or (2) is configured such that the second means can be freely and continuously controlled near or remotely from the lens body. Automatic aperture control device for lenses for (4) In the device according to claim +11, (2) or (3), the aperture value once set under an arbitrary power supply voltage is stabilized by stabilizing the control signal to a potential that is half the power supply voltage. An automatic aperture control device for a CCTV camera lens, characterized in that a third means is configured so that the aperture is always kept constant.